Somatosensation, Mechanoreceptors, and Thermosensation

Piezo1 and Piezo2 are examples of

Mechanoreceptors

Mechanorecptors are opened by

a mechanical force that physically pulls the channel open

Piezo channels are predicted to have >30 ______

transmembrane domains

Purified Piezo proteins reconstituted in artificial lipid bilayers form ion channels that

transduce tension in the surrounding membrane

Merkel cells:

- Found at the surface of the skin

- Slowly adapting

- small receptive fields

- 25% of receptors in hand

- E.g reading braille

Meissner's Corpuscles

- Rapidly adapting

- Located in superficial skin in hairless areas (lips, palm, etc)

- Small receptive fields

- Low frequency vibrations and light touch

- ~40% hand

- E.g tickle of a feather

Pacinian corpuscles

- Rapidly adapting

- Located in deeper tissue

- Large receptive fields

- Respond to high frequency vibrations

- E.g texture sensing; tool usage

Pacinian corpuscles have rapidly adapting layers that have to reset before they can be used again

This is true

Ruffini endings

- Slow adapting

- Located deeper in skin

- Large receptive fields

- Detect deep sustained pressure and stretch

- E.g feeling of massage

The ruffini endings are the predominating touch receptor in the

Periodontal ligament

Since ruffini endings are slow adapting why would you want them in the periodontal ligament

You want to know for biting. Is there pressure are we biting down on something. Are we biting something I don't want to be.

Hair follicle receptors

- Rapidly adapting

- Present only in hairy skin

- Senses movement of hair on skin and very light touch

- E.g rubbing cotton lightly on arm

Review: What does it mean to have a rapid adapting versus a slow adapting touch receptor

Slowly adapting receptors: Keep firing as long as stimulus is present

Fast adapting receptors: Fire only at start/stop or changes in stimulus

Summary: Meissner

Field: Small

Adapt: Rapid

Summary Merkel

Field: Small

Adapt: Slow

Summary Pacinian

Field: Large

Adapt: Rapid

Summary Ruffini

Field: Large

Adapt: Slow

Detect where limbs (and other body parts) are in space

Proprioceptive mechanoreceptors

There are specialized proprioceptors in the

head and heart

Groups of specialized intrafusal muscle fibers surrounded by a capsule of connective tissue

Muscle spindles

Temperature detection

Thermosensation

Thermosensation tiggers reflex to

withdraw from painful heat or cold

Humans can sense about _ ranges in temperature

7

We only have __ types of temperature receptor sensors

4

What are the 4 types of temperature receptor sensors

Cold nociceptor: activated from 5-15 degrees celsius

Cool receptor: peak activity at 24 degrees celsius

Warm receptor: peak activity at 42 degrees celsius

Hot nociceptor: activated above 45 degrees celsius

The TRPV1 channel responds to

heat

chemical signals such as capsaicin

Other TRP channels respond to

different temperatures

Heat opens the TRPV1 channel pore by

displacing membrane lipids surrounding the channel, the structural rearrangement then opens cation channel gates

Different receptors activate at different

temperature

Distribution of activity is not

uniform for the receptors

Combing the signals from all 4 receptors gives us

a sense of the overall temperature

Combing the signals from all 4 receptors gives us a sense of the overall temperature. This is termed?

Combinatorial code

ADD card Labeled lines review - you took screenshot- 17:41 of video

Hey you finish this card

Touch and pain take

separate pathways to the Brain

What happens in the case of spinal cord lesions

Its going to impact pain and touch very different depending on where in the spinal cord that lesion is

Example

Lower thoracic: Lesioning some type of pain and some type of touch but they will impact different sides of the body.

Major pathways of pain Head and face has three branches:

Ophthalmic

Maxillary

Mandibular (both sensory and motor fibers)

Pain and temperature from all 3 branches enter

CNS at pons and descend to medulla and cervical regions

________ of the trigeminal nerve- very long nucleus where pain and temperature fibers synapse on second order neuron

Spinal nucleus

These neurons _____ and project to thalamus as well as reticular formation and PAG

decussate

Chemoreception

Taste and Smell

Our chemical senses are intimately linked with neural circuits that

control emotion motivational state, and memory (Limbic System)

Quality control intake of environment cues

Gastrointestinal system

Taste and smell are chemical senses

Chemoreceptors generate neural signals on binding with particular chemicals in the environment

There is a large amount of overlap in perception of

Taste and smell

Molecules that can be tasted are detected by taste cells clustered in

taste buds

Taste receptors are modified

epithelial cells

Anatomy of taste buds: _____allows microvilli of the receptor cells to have access to the surface of the tongue

Taste pore

Anatomy of taste buds: Dying receptor cells can be replaced with the

differentiation of support cell

Anatomy of taste buds: ~ ____-____ Taste receptors

50-100

Anatomy of taste buds: Taste receptors do NOT fire __________ but release ATP as a neurotransmitter on _________

Action Potential, cranial nerve fibers

Anatomy of taste buds: Receptors have lifespan of

10 days

Anatomy of taste buds: Cilia or microvilli protrude

slightly through pore

Anatomy of taste buds: Tastants dissolve in liquid com in contact with the

surface of receptors

Anatomy of taste buds: Plasma membrane of cilia have receptors that

bind molecular tastants

Anatomy of taste buds: Tastant binding depolarizes the cell triggering

voltage gated Ca channel opening, entry of Ca and release of NT

Salt taste-

Direct entry of sodium ions through sodium ion channels causes receptor depolarization in response to salt

Sour taste-

Caused by acids (H+ ions) which enter the cell through cation channels and blocks outward flow of K+. Both of which contribute to depolarization.

Sour taste receptor identified in 2006 as a

TRP channel (named PKD2L1)

Is this important?

- No freaking idea

- Probably not

- If it's on the test then I think they just hate us

- But if it is we will all get it right because it's on this card ;)

Sweet taste-

Glucose and other organic molecules with similar structures bind to a receptor and activates a G-protein coupled signaling cascade. Closing K+ channel = Depolarization

Bitter taste-

The only taste caused by a diverse group of (~30) tastants. Mediated by G-protein coupled signals. Gustducin is one example of bitter receptor

Umami Taste

Caused by amino acids such as glutamate. Responsible for distinctive flavor of MSG. Mediated by a G-protein coupled signal

Fat ?????????????????

A taste receptor that binds to fatty acid chains was recently identified and is proposed as a possible 6th taste

The identity, concentration, and valence value of tastants is conveyed to brain by

action potentials of taste buds

Neurons likely tune to specific

tastants

Transduction: _____ is the primary NT released from taste buds to communicate with gustatory nerves

ATP

Although each taste bud preferentially responds to one taste, every taste bud also responds to a

lesser degree to each other taste- allowing many subtle variations in response

Taste cells synapse with

primary sensory axons that run in the chorda tympani

Cranial nerve VII (facial nerve) =>

taste buds in the tongue

Cranial nerve IX (glossopharyngeal nerve) =>

Taste buds of the palate

Cranial nerve X (Vagus nerve) =>

taste buds to the epiglottis, and esophagus

The cranial nerves that are responsible for taste all go to

Nucleus of the solitary tract (medulla)

The nucleus of the solitary tract contains interneurons synapse on vagus nerve connecting taste with gastrointestinal system in a

Gustatorial-gastrointestinal reflex arc

Subjective awareness of external world and self

Consciousness

Conscious interpretation of the external world by the brain from patterns of nerve impulses from sensory receptors

Perception

We can only perceive what

have receptors to detect (we don't have infra-red receptors)

Sensory inputs get altered/removed during

sensory processing (thalamic processes)

Higher cortical processes (cortical integration) alter perception based on

contexts and prior experiences

There are 2 major divisions of the nervous system:

The central nervous system= Brain, Brainstem, and spinal cord

The peripheral nervous system= afferent and efferent fibers

Bidirectional information flows

CNS<->PNS

There are two directions for information in PNS

Afferent division: Going to the CNS

Efferent division: Exiting the CNS

Refers to the limitation of receptors you have. You can only detect stimuli for which you have detectors, thus, although you receive stimuli in the ultraviolet and infrared regions you have nothing that can detect these stimuli and so you are ignorant of this information

Detection limitation

Is what the brain must do in order to make sense of the sensory information it is receiving. The brain does this by comparing information it is receiving with information it has received in the past. Basically, the brain creates a best guess scenario of what is happening in the present

Prior experience

Perception or awareness of the inner state of the body such as heart rate, hunger, thirst, etc

interroception

The cells that can detect a given modality of a stimulus

Sensory receptors

Each sensory receptor cell responds to

a specific stimulus or modality

The basic sensory modalities include

light, sound, taste, temperature, pressure, and smell

The stimulus modality that a given sensory receptor is specialized to detect

Adequate stimulus

Your photoreceptors are supposed to respond to ___ this is there adequate stimulus, but this doesn't mean in a high stimuli setting they can't respond to other stimuli (like touch or pressure etc)

light

What dictates the stimulus intensity of an action potential

The magnitude of the stimulus (the stronger the stimulus the higher intensity of the stimulus)

Stimulus intensity =

frequency of action potentials and the number of neurons responding

- Involves a mechanical action such as skin deforming/movement or other physical changes in nerve endings, altering ion permeability => action potentials

Mechanosensation

Mechanosensation includes

- Skin

- Organs

- Proprioception

Where your muscles are in space

Proprioception

_____ fiber terminals detect and transmit touch sensory stimuli

Afferent

Mechanoreceptors are critical for monitoring a variety of physiological activities:

- Touch

- Proprioception

- Hearing

- Balance

- Blood pressure

____ and ___ have free nerve endings i.e. non-myelinated terminal branches that ramify widely in upper regions of dermis

Nociceptor and thermoceptors

____ are "encapsulated" and have lower thresholds for action potentials

Cutaneous mechanoreceptors

What is happening with one receptor cell can

Influence whats happening with its neighbor cell

When you have lateral inhibition

You have additional inhibitor neurons that are going to influence sending the signal to the next neuron. The neuron that is simulated the most is going to inhibit the ones next to it.

Why is lateral inhibition helpful

It is increasing the acuity of the response

⌄⌄Without stupid science terminology ⌄⌄

It is more precise [makes it so the receptors next to the one actually being effected don't also respond]